This invention relates to densely packaged electronic signal processing circuits which provide maximum signal manipulation closely adjacent to multiple analog signal generators.
In certain situations it is very desirable to complete several signal manipulations in each of a plurality of parallel channels on a single chip, which is immediately adjacent to a plurality of analog signal transducers. An important advantage can be provided by accomplishing analog to digital conversion in each on-chip channel.
The field of current primary interest is photodetector arrays, whose output efficiency is enhanced by minimizing the signal processing which is located remote from the photodetector arrays, and maximizing the signal processing which occurs "at the focal plane". Usually, but not always, the distinction between "on focal plane" (close proximity) and "off focal plane" (remote) signal processing is determined by the fact that the former is located in an artificially cooled environment (e.g., inside a Dewar), whereas the latter is not in an artificially cooled environment.
However, other types of transducer arrays, e.g., audio, temperature, and pressure, may benefit from the concepts of the present invention. In general, the arrays and their parallel electronic channels are characterized by limited available real estate, and by the need to maintain low power operation. Noise corruption of the signals may be a problem if the conversion to digital signals is remote from the analog transducers.
Developments leading to the problem-solving which motivated the present invention were primarily in the field of "Z-technology", a field pioneered by the assignee of the present invention. (See U.S. Pat. Nos. 4,490,626; 4,551,629; 4,555,623; and 4,672,737.)
In Z-technology, photodetectors are spaced along the focal plane in both X and Y dimensions, and electronic circuitry is buried in a stack of IC chips extending in the Z dimension. In the prior patents referred to, Z-technology modules are disclosed in which the photodetector signals are pre-amplified, filtered, and multiplexed in a cooled environment, before the signals are transmitted to more remote electronic equipment. The pre-multiplexing and multiplexing functions are performed within the Z dimension, in order to improve electronic performance and simplify electrical connections between the focal plane modules and the non-focal plane circuitry.